why give up OVF with MirrorLess camera like Nex

What helped me with EVF cameras is disable image review. It is highly distracting and increases blackout time.

Need a camera that only sends review image to rear monitor but still allows live viewfinder feed.

Most live view cameras with image review disabled are much more usable. You generally don't need review images anyway since you know exactly what your final image will look like from the EVF (a good EVF should be WYSIWYG), with the exception of flash. In those cases review every 5 or 10 images to make sure your exposure is still close.